It is known to use drill pipe or coiled tubing to drill wellbores or to service existing wells to remove fill such as sand, scale, or other deposits in tubular members in the wellbore. It is desirable to remove drill cuttings in drilled wells or fill and deposits in existing wells to establish, restore, or improve the production of oil or gas or both from subterranean formations intersected by the wellbore. Generally in industry, removal from a wellbore of cuttings, fill, scale particles, other deposit particles, sand, and the like, collectively referred to herein as solids, is called well cleanout. Other reasons that removal of solids from a wellbore is desirable include to permit passage of wireline or service tools in the borehole, ensure the proper operation of downhole flow control devices, and remove material which may interfere with subsequent well service or completion operations.
The success of a cleanout operation normally is judged based on the reduction of the amount of solids in a borehole after cleanout. Cleanout job efficiency is a term that relates the reduction of the solids in a borehole after cleanout compared to the quantity of solids present in the borehole prior to the cleanout operation. The quantity of solids before and after a cleanout operation typically are estimated based on well configuration, pump rates, fluid properties, performance history, modeling, and field experience in similar situation among other factors, not on measurement. A method of reliably determining the quantity of solids present before and after a cleanout operation based on measurement or a measured characteristic indicative of the presence of solids is desirable.
Many factors affect cleanout efficiency and effectiveness; some of these factors specifically relate to the transport of wellbore solids from the wellbore during cleanout efforts. Discussions on solids transport in wellbores are presented in Cuttings Transport Problems and Solutions in Coiled Tubing Drilling, Leising, L. J, and Walton, I. C., IADC/SPE 39300, Mar. 3-6, 1998, pp 85-100, Optimizing Cuttings Circulation in Horizontal Well Drilling, Martins, A. L. et al., SPE 35341, March 1996, pp 295-304; and State-of-the Art Cuttings Transport in Horizontal Wellbores, Pilehvari, Ali A. et al., SPE 39079, November 1995, pp 389-393, each of which is incorporated herein in the entirety by reference. Wellbore characteristics such as temperature, pressure, and configuration can affect cleanout efforts; deviated and horizontal wells generally are more difficult to cleanout than vertical wells. Characteristics of the cleanout fluid are another factor. In addition, the characteristics of the wellbore solids such as particle size, shape and density may affect cleanout efficiency.
Computer models and simulators are known for use in modeling and simulating a well cleanout operation. Examples of such are presented in Development of a Computer Wellbore Simulator for Coiled-Tubing Operations, Gu, Hongren and Walton, I. C., SPE 28222, July 1994; Computer Simulator of Coiled Tubing Wellbore Cleanouts in Deviated Wells Recommends Optimum Pump Rate and Fluid Viscosity, Walton, I. C., SPE 29491, April 1994; and Two New Design Tools Maximize Safety and Efficiency for Coiled Tubing Pumping Treatments, SPE 29267, Gary, S. C. et al., March 1995, each of which are incorporated by reference herein in the entirety.
Typically a well cleanout operation is considered a success if it results in increased well production or improved well access for performing subsequent wellbore operations. These operational improvements however are not readily observable or manifest during or immediately after the performance of a cleanout operation. As such, they do not provide a real time indicator as to whether or not a cleanout operation has been successfully performed throughout a wellbore. Similarly, existing methods known for use in determining the presence of solids in a wellbore, such as running a video camera or mechanical probe downhole, are not applicable for use during a clean out operation. An apparatus and methods to determine the success of a well cleanout operation in real time is needed to provide an operator with information expediently to determine if additional cleanout efforts are needed while the cleanout equipment and personnel are at the well site, thereby avoiding time and scheduling delays as well as the expense of remobilization in the event that additional cleanout efforts are required. The present invention addresses these needs.